Macrophage stimulating protein (MSP), a component of mammalian blood plasma, makes mouse peritoneal macrophages responsive to chemoattractants such as complement C5a [Leonard et al., Exp. Cell Res. 102:434 (1976) and Leonard et al., Exp. Cell Res. 114:117 (1978)]. MSP also stimulates mouse macrophages to increase their movement and pinocytic activity.
The discovery of MSP was based on the observation that peritoneal macrophages in RPMI 1640 medium did not migrate to C5a unless serum was added to the cell suspension. Sera from different mammals, including mice and man, caused activation.
The low concentration of MSP in serum (less than 1/10.sup.5 of total serum protein) precluded complete purification by conventional techniques. However, highly purified MSP is required for use in human treatments. A method resulting in highly purified MSP is desirable.